Rendering proper materials
LookDev mode is intended to give a basic approximation of how the material will behave. Those reflections? They're a built-in environment texture so that we can see the reflections of the surface. Rendering is a different process tho, and uses separate lighting. 

Lighting is a pretty complex topic, but one good way to get reliable results is to use an HDRI - like lookdev mode does. Hdris can easily provide good lighting and realistic reflections. This is perfect in your case too, because the reason that the rendered sphere looks flat is because it only has a uniform color to reflect! The best free high-quality HDRI source is hdrihaven.com To learn about how to use them in your scene, see this How can I render an object with an hdr background?

I hope this helps!